1,4-Dihydropyridines: discovery of minimal AIEEgens and their mitochondrial imaging applicationsElectronic supplementary information (ESI) available: Syntheses and characterisation data (1H NMR, 13C NMR, mass spectra), experimental details, and additional spectroscopic data and images. CCDC 1424322, 1424344 and 1424354. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6tb02135b

Typical aggregation-induced emission enhancement fluorogens (AIEEgens) generally are designed as propeller-shaped molecules with multiple aromatic rotors. Described herein are 1,4-dihydropyridines, which have the minimum size necessary for AIEE, containing only a single ring, synthesized through a facile biocatalysis procedure. Owing to the AIEE property, intramolecular motion can be restrained by the surrounding environment, causing the radiative channel to open up. Both the fluorescence intensities and the lifetimes of the 1,4-dihydropyridine representatives increased with increasing viscosity, and high sensitivities were observed. On the basis of the single crystal X-ray structures, density functional theory (DFT) calculations were performed to explain the mechanism of the single-ring AIEE behaviour. Moreover, a few of the neutral AIEEgens were found to possess a high specificity towards mitochondria. As an example, one of the AIEEgens exhibited superior photostability and excellent storage tolerance, allowing for real-time imaging, viscosity mapping, and long-term tracking of the dynamics of the mitochondrial morphology. Minimal AIEEgens containing only a single ring were synthesized through a facile biocatalysis procedure and were successfully utilized in the imaging of mitochondria.